Abstract:This report describes the development, differentiation and maturation of the gonad in Tilapia mossambica. Through histological studies, mainly there are three stages canbe divided. 1. The newly hatched fry before the yolk sac is absorbed, there are only a fewprimordial germ cells observed at the root of coelomic membrane between themesonephric duct, dorsal aorta and the gut. 2. Sex remains undifferentiated 10 days after hatching,and when the fry attains 9mm in total length, the gonadal anlage usually differentiated into two types. The broadones develop more rapidly, and contain many germ cells, some of which show mitoticphase. The other is small and narrow, which contains only 2 or 3 germ cells without anymitotic phase. 3. At the stage of 30 days after hatching, when the fry attains to 25 mm in totallength, the germ cells of the large gonadal anlage enter into the early oocyte stage andfurther develop to form ovary. While the germ cells of the small gonadal anlage justbegin to enter the mitotic phase, they will develop into testis later. So that the differen-tiation of the testis is about 20 days later than that of the ovary. The ovary and thetestis mature at the stage of 90 days after hatching. For the purpose of sex inducement in Tilapia mossambica, it is suggested that theprocess is better to operate before the fry reaches to the length of 9 mm, and so thesuccess may be more reliable.

Abstract:This paper is a study, on small-scale Reynolds similarity criterion for model testof the trawl--net. After analysing the theoretical basis for current similaritycriteria, it gives a new similarity criterion based on small-scaled Reynolds similarity. 1. The main differences between the two kinds of criteria are as follows: (1) The current criteria do not consider the viscous force similarity. They supposethat the coefficient of net resistance is a constant, and the net resistance is proportionalto the square of velocity. In this criterion. we consider the coefficient of net resistanec (C_R) is not a constant but a function of Reynolds number, and then the viscous forcesimilarity criterion should be considered. (2) In the current criteria, the relation between the velocity of model net and fullscale net is introduced according to the gravity force similarity. But, according to thefilter-flow speciality of net, we think viscous force is the most important one for netresistance. We take the small-scaled Reynolds numbers similarity as a basis forintroducing the relation between the velocity of model net and full scale net. Simul-taneously, a revision coefficient (C₁) is introduced to consider the difference betweentwo large-scaled Reynolds numbers. 2. In this paper, the main points of the criterion are pointed out. The relationsbetween model net and full scale net are as follows: Large scale rstio: l₁/l₂ = b₁/b₂ =H₁/H₂=... = λ Small scale ratio: d₁/d₂ =a₁/a₂ = S₂'~(1/2)/S₂'~(1/2)=...=λ' Large-scaled Reynolds numbers: Re₁ = V₁l₁/v₁, Re₂ = V₂l₂/v₂ Small-scaled Reynolds numbers: Re₁' = V₁d₁/v₂, Re₂'= V₂d₂/v₂ The two small--scaled Reynolds numbers are equal: Re₁' = Re₂' The two large--scaled Regnolds numbers are not equal: Re₁≠Re₂ The relation between two velocities: V₂ = V₁λ' The formu1as of net resistance: R₁ = 1/2ρ₁V₁²Ω₁C(R₁), R₂ = 1/2ρ₂V₂²Ω₂C_(R₂) The relation between two resistance coefficients: C(R₁)=C₁C_R The coefficient C₂ is a revision coefficient. It considers the difference between twolarge-scaled Reynolds numbers. If Re₂'≥Re_(kp), C₁→1, Re_(kp) is a critical Reynolds number. In the above, "1" is for full scale net; "2" is for model net.

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Abstract:This article discusses the race, migration, growth pattern, mortality and dynamicsof the herring (Clupea harengus pellasi Valenciennes) inhabiting in Huang Hai, andattempts to make prediction and management on fisheries. The results are summarizedas follows: 1. IIerring inhabiting in areas north to the latitude of 34°in Huang Hai all the year round it is believed to be a race of the Pacific herring. Hence they are traditionallycalled the Huang Hai herring. 2. The growth pattern of Huang Hai herring can be described by von Bortalanffyequation, and as of year 1972 the value of parameters for the equation is IV_∞ = 314g.,L_∞ = 308mm, and K = 0. 58. The maximum growth rate appears at t = 1.3 years. FromFebruary 1972 to March 1973, the total Instantaneous mortality estimated by data forthe catch per effort was 1.05 which consists of the fishing mortality 0. 939 and thenatural mortality 0. 111. 3. The numbers of the 1970 year-class in early January were estimated with twoprocesses, Delury's method and the method of estimation of fishing mortality. The dif-ference in valuo of the calculation between the two methods is about 5%. the averagevalue is 2082×10⁶ individuals, it coincides with actual catches as shown in the table 6. 4. In the 1970s, the fluctuation in the numbers of the population happened to be maximum in the year of 1972 and minimum in 1977. The former were ten times greaterthan the latter. These drastic dynamics were considered to be a natural phenomenon rather than the result of over-fishing. The statistical analysis shows the interdependencebetween actual catches and the abundance index obtained from fish--searching in October. The relative coefficient was 0. 9710. 811 (P0. 05), which accounts for thefact that catches can be predicted by abundance.index. 5. After making a careful study of the optimal fishing mortality and mesh--sizefor the fisheries, and considering the economical value of the herring eggs, we workedout a strategy on the management of the fisheries for Huang Hai herring. Since thevalue(including the yield, average body length and weight as well as the age of the 1970year-clase) obtained by Boverton-Holt model and S--E model are similar to the resultssampled from fishcries, it is suggested that the conclusion here submitted in the papermay be valid.

Abstract:A Iarge mumber of fishes in the East China Sea have the behavior of verticalmigration. In attempting to increase the fishing efficiency, a large-mesh trawlhas been designed for catching the fish in the higher level above than the normaltrawl can reach. From December 1977 to July 1978, the large--mesh trawl has beentested in comparison with the normal trawl. The result indicates that the large-meshtrawl has some advantages, such as higher trawl net mouth, less resistance, morecatches, etc.

Abstract:There are 983 and 1200 hairtail fish (Trichiurus haumela Forskal) used respectivelyfor age analysis and for composition analrsis. Samples were taken in Po Hai and HuangHai in 1962--1963. The results are summarized as follows: 1) The hairtail fish in Po Hai and Huang hai grow rapidly in the same year theyhatched. The body length reaches 72mm about two months after hatching, and at thelength of 190mm the annulus begins to form. Therefore the first annulus obsreved canbe considered as the first true annulus. 2) The relationship between body length (L) and distance of the annulus from thenueleus (R) on the otolith is conformed with the power function curve: L = 36. 84R^{(1. 595x)} 3) The growth of the hairtail fish is as the following cquations: L_t = L_∞[1 - e^-K(t-t₀))].where L_∞ = 501mm; K= 0.438; t_0 = - 0. 0607 W_t = W_∞[1 -e^(K(t-t₀)]³.where W_∞ = 1592g; K= 0. 34; t = - 0.91 The coordinate of the inflexion point being at t = 2. 32 W_t = 471, corresponding to 0.232 W. 4) The Length (L) weight (W) relationship of the hairtail fish is expressed as fol-lows: W = 3. 339×10~(-6)L^(2.8445) 5) It is certain that the monthly changes of the terminal index at each annulusgroup of the otolith form one cycle each year. The terminal margin of the opaque zone(narrow zone) is called the annulus and the formation of the annulus chiefly takes placefrom January to March.

Abstract:The purpose of this article is to make a brief review on the relationship between thedistribution of zooplankton and fishing grounds of mackerels (Pneumatophros japonicus)and scads (Decapterus maruadsi) based upon the materials collected in 1972--1975.Theses fishes are mainly zcoplankton feeders and also take a little amount of young orsmall fishes. The main coustituents of the food of these fishes are Euphausia pacifica,Calanus sinicus, Laptochela aculeocadata, Parathemisto gavdichaudi etc. It has beenfound that in spring the spawning shoals usually aggregate in the coastal water ofZhejiang Province, where it is rich in zooplankton and the fishes take plenty of foodbefore or after spawning The fishing center coincides usually with abundant zone ofbiomass especially aggregation of Calanus sinicus and Euphausia pacifica. The shoals migrate gradually northeastward and some mackerel schools enter Huang Hai, while thewarm current and the food organisms zone move continuosly along the Zhejiang coast.The feeding grounds of these fishes are situated in the western part of the Kyushu,south western waters of the Chiju Island and near the mouth of Chang Jiang, wherethere is plenty of food organisms. In the late Autumn, with the water temperaturelowering down there is they gradually migrate the wintering ground in the southeastern region of the Dong Hai and it is under the influence by Kuroshio or Taiwancurrent. In this region the food and hydrographic conditions are most favourable tothe aggregation of these schools, so that a fine fishing ground is formed there

Abstract:The behavier of shrimps is that they keep hidden at day while active at night, sothat the yield of the traditional shrimp catching at night is much higher than at day- time. For the purpose increase yield at the daytime, fishing engineers in our countryand abroad attempt to improve the fishing gear by the combination of electrical deviceswith nets. It seems effective in shrimp catching. By analysing the data derived from tbe electrical experiments of more than 700Penaeut mesquiensis, this article emphatically deals with the physiological response ofshrimps to different electrical strength and it is found that the optimal electrical intensityfor driving shrimps from substratum is a D. C. pulsation at 1--5 IIz (frequency) and theelectrodes are apart 0. 2--1. 0 M (width); but it is variable with the length of shrimps andthe angle of direction in electrical field. Other aspects relate to electrical device withdifferent powers, and the information of distribution in field intensity caused byelectrodes are also discussed